Lubricating composition

ABSTRACT

A lubricating composition for use in the crankcase of an engine comprising a base oil and one or more additives, wherein the lubricating composition comprises from 0.01 wt % to 5 wt %, by weight of the lubricating composition, of one or more liquid crystal compounds, wherein the one or more liquid crystal compounds is a terphenyl compound. 
     The lubricating composition provides improvements in terms of reduced friction and wear, in addition to improved fuel economy performance.

This non-provisional application claims priority from U.S. ProvisionalApplication Ser. No. 61/815,011 filed Apr. 23, 2013, which is herebyincorporated by reference in its entirety.

The present invention relates to a lubricating oil composition, inparticular to a lubricating oil composition which is suitable forlubricating internal combustion engines and which has improved frictionand wear reduction and improved fuel economy.

Increasingly severe automobile regulations in respect of emissions andfuel efficiency are placing increasing demands on both enginemanufacturers and lubricant formulators to provide effective solutionsto improve fuel economy.

Optimising lubricants through the use of high performance basestocks andnovel additives represents a flexible solution to a growing challenge.

Friction-reducing additives (which are also known as friction modifiers)are important lubricant components in reducing fuel consumption andvarious such additives are already known in the art.

Friction modifiers can be conveniently divided into two categories, thatis to say, metal-containing friction modifiers and ashless (organic)friction modifiers.

Organo-molybdenum compounds are amongst the most common metal-containingfriction modifiers. Typical organo-molybdenum compounds includemolybdenum dithiocarbamates (MoDTC), molybdenum dithiophosphates(MoDTP), molybdenum amines, molybdenum alcoholates, and molybdenumalcohol-amides. WO-A-98/26030, WO-A-99/31113, WO-A-99/47629 andWO-A-99/66013 describe tri-nuclear molybdenum compounds for use inlubricating oil compositions.

However, the trend towards low-ash lubricating oil compositions hasresulted in an increased drive to achieve low friction and improved fueleconomy using ashless friction modifiers.

Ashless (organic) friction modifiers which have been used in the pasttypically comprise esters of fatty acids and polyhydric alcohols, fattyacid amides, amines derived from fatty acids and organic dithiocarbamateor dithiophosphate compounds.

However, current strategies with regard to friction reduction for fueleconomy oils are not sufficient to meet ever increasing fuel economytargets set by Original Equipment Manufacturers (OEMs).

For example, molybdenum friction modifiers typically outperform ashlessfriction modifiers in the boundary regime and there is a challenge toapproach similar levels of friction modification using solely ashlessfriction modifiers.

Thus, given the increasing fuel economy demands placed on engines, thereremains a need to further improve the friction reduction and fueleconomy of internal combustion engines utilising low ash lubricating oilcompositions.

Liquid crystalline components have not attracted as much attentionwithin the field of lubrication as have more conventional chemicaladditives.

WO99/24533 discloses a friction reducing lubricant compositioncomprising a liquid crystal and a surfactant.

EP-A-567 649 discloses an electroviscous fluid containing an antioxidantand/or a metal corrosion inhibitor or solid particles as a dispersoid inan electrically insulating fluid as a dispersion medium consistingprincipally of a liquid crystal substance. Example 3 contains a mixturesof four liquid crystal substances namely: 4-cyano-4′-pentyl-biphenyl,4-cyano-4′-septyl-biphenyl, 4-cyano-4′-octyloxy-biphenyl, and4-cyano-4′-pentyl-terphenyl.

There has now been surprisingly found in the present invention alubricating oil composition comprising ashless friction modifiers whichhas good friction and wear reduction and improved fuel economy.

Accordingly, the present invention provides a lubricating compositionfor use in the crankcase of an engine comprising a base oil and one ormore additives, wherein the lubricating composition comprises from 0.01wt % to 5 wt %, by weight of the lubricating composition, of one or moreliquid crystal compounds, wherein the one or more liquid crystalcompounds is a terphenyl compound.

By “liquid crystal” it is meant highly anisotropic fluids that existbetween the boundaries of the solid and conventional isotropic liquidphase. The phase is a result of long-range orientational ordering amongconstituent molecules that occurs within certain ranges or temperaturein melts and solutions of many organic compounds.

The one or more liquid crystal compounds is present in the lubricatingcomposition at a level of from 0.01 wt % to 5 wt o, preferably from 0.01wt % to 4 wt %, more preferably from 0.1 wt % to 2 wt %, and especiallyfrom 0.2 wt % to 1 wt %, by weight of the lubricating composition.

Preferred terphenyl compounds for use herein include cyanoterphenylcompounds such as alkylterphenylnitriles and alkyletherterphenylnitrilesand mixtures thereof.

Suitable terphenyl compounds for use herein have the following generalformula I:

wherein X is CN, and R is a C₁-C₂₂ alkyl or C₁-C₂₂ alkylether group.Preferably the R group is a C₁-C₂₂ alkyl group, more preferably a C₄-C₁₆alkyl group and even more preferably a C₅-C₁₀ alkyl group.

A particular preferred liquid crystal compound for use herein is4-cyano-4′-pentyl-terphenyl. This compound is commercially availablefrom Alfa-Aesar under the designation “T15”.

The total amount of base oil incorporated in the lubricating oilcomposition of the present invention is preferably present in an amountin the range of from 60 to 92 wt. %, more preferably in an amount in therange of from 75 to 90 wt. % and most preferably in an amount in therange of from 75 to 88 wt. %, with respect to the total weight of thelubricating oil composition.

There are no particular limitations regarding the base oil used in thepresent invention, and various conventional known mineral oils andsynthetic oils may be conveniently used.

The base oil used in the present invention may conveniently comprisemixtures of one or more mineral oils and/or one or more synthetic oils.

Mineral oils include liquid petroleum oils and solvent-treated oracid-treated mineral lubricating oils of the paraffinic, naphthenic, ormixed paraffinic/naphthenic type which may be further refined byhydrofinishing processes and/or dewaxing.

Naphthenic base oils have low viscosity index (VI) (generally 40-80) anda low pour point. Such base oils are produced from feedstocks rich innaphthenes and low in wax content and are used mainly for lubricants inwhich colour and colour stability are important, and VI and oxidationstability are of secondary importance.

Paraffinic base oils have higher VI (generally >95) and a high pourpoint. Said base oils are produced from feedstocks rich in paraffins,and are used for lubricants in which VI and oxidation stability areimportant.

Fischer-Tropsch derived base oils may be conveniently used as the baseoil in the lubricating oil composition of the present invention, forexample, the Fischer-Tropsch derived base oils disclosed in EP-A-776959,EP-A-668342, WO-A-97/21788, WO-00/15736, WO-00/14188, WO-00/14187,WO-00/14183, WO-00/14179, WO-00/08115, WO-99/41332, EP-1029029,WO-01/18156 and WO-01/57166.

Synthetic processes enable molecules to be built from simpler substancesor to have their structures modified to give the precise propertiesrequired.

Synthetic oils include hydrocarbon oils such as olefin oligomers (PAOs),dibasic acids esters, polyol esters, and dewaxed waxy raffinate.Synthetic hydrocarbon base oils sold by the Royal Dutch/Shell Group ofCompanies under the designation “XHVI” (trade mark) may be convenientlyused.

Preferably, the base oil comprises mineral oils and/or synthetic oilswhich contain more than 80% wt of saturates, preferably more than 90%wt., as measured according to ASTM D2007.

It is further preferred that the base oil contains less than 1.0 wt. %,preferably less than 0.1 wt. % of sulphur, calculated as elementalsulphur and measured according to ASTM D2622, ASTM D4294, ASTM D4927 orASTM D3120.

Preferably, the viscosity index of the base fluid is more than 80, morepreferably more than 120, as measured according to ASTM D2270.

Preferably, the lubricating oil composition has a kinematic viscosity inthe range of from 2 to 80 mm²/s at 100 ° C., more preferably of from 3to 70 mm²/s, most preferably of from 4 to 50 mm²/s.

The total amount of phosphorus in the lubricating oil composition of thepresent invention is preferably in the range of from 0.04 to 0.12 wt. %,more preferably in the range of from 0.04 to 0.09 wt. % and mostpreferably in the range of from 0.045 to 0.08 wt. %, based on totalweight of the lubricating oil composition.

The lubricating oil composition of the present invention preferably hasa sulphated ash content of not greater than 2.0 wt. %, more preferablynot greater than 1.0 wt. % and most preferably not greater than 0.8 wt.%, based on the total weight of the lubricating oil composition.

The lubricating oil composition of the present invention preferably hasa sulphur content of not greater than 1.2 wt. %, more preferably notgreater than 0.8 wt. % and most preferably not greater than 0.2 wt. %,based on the total weight of the lubricating oil composition.

The lubricating oil composition of the present invention may furthercomprise additional additives such as anti-oxidants, anti-wearadditives, detergents, dispersants, friction modifiers, viscosity indeximprovers, pour point depressants, corrosion inhibitors, defoamingagents and seal fix or seal compatibility agents.

Antioxidants that may be conveniently used include those selected fromthe group of aminic antioxidants and/or phenolic antioxidants.

In a preferred embodiment, said antioxidants are present in an amount inthe range of from 0.1 to 5.0 wt. %, more preferably in an amount in therange of from 0.3 to 3.0 wt. %, and most preferably in an amount in therange of from 0.5 to 1.5 wt. %, based on the total weight of thelubricating oil composition.

Examples of aminic antioxidants which may be conveniently used includealkylated diphenylamines, phenyl-α-naphthylamines,phenyl-β-naphthylamines and alkylated α-naphthylamines.

Preferred aminic antioxidants include dialkyldiphenylamines such asp,p′-dioctyl-diphenylamine, p,p′-di-α-methylbenzyl-diphenylamine andN-p-butylphenyl-N-p′-octylphenylamine, monoalkyldiphenylamines such asmono-t-butyldiphenylamine and mono-octyldiphenylamine,bis(dialkylphenyl)amines such as di-(2,4-diethylphenyl)amine anddi(2-ethyl-4-nonylphenyl)amine, alkylphenyl-1-naphthylamines such asoctylphenyl-1-naphthylamine and n-t-dodecylphenyl-1-naphthylamine,1-naphthylamine, arylnaphthylamines such as phenyl-1-naphthylamine,phenyl-2-naphthylamine, N-hexylphenyl-2-naphthylamine andN-octylphenyl-2-naphthylamine, phenylenediamines such asN,N′-diisopropyl-p-phenylenediamine andN,N′-diphenyl-p-phenylenediamine, and phenothiazines such asphenothiazine and 3,7-dioctylphenothiazine.

Preferred aminic antioxidants include those available under thefollowing trade designations: “Sonoflex OD-3” (ex. Seiko Kagaku Co.),“Irganox L-57” (ex. Ciba Specialty Chemicals Co.) and phenothiazine (ex.Hodogaya Kagaku Co.).

Examples of phenolic antioxidants which may be conveniently used includeC7-C9 branched alkyl esters of3,5-bis(1,1-dimethyl-ethyl)-4-hydroxy-benzenepropanoic acid,2-t-butylphenol, 2-t-butyl-4-methylphenol, 2-t-butyl-5-methylphenol,2,4-di-t-butylphenol, 2,4-dimethyl-6-t-butylphenol,2-t-butyl-4-methoxyphenol, 3-t-butyl-4-methoxyphenol,2,5-di-t-butylhydroquinone, 2,6-di-t-butyl-4-alkylphenols such as2,6-di-t-butylphenol, 2,6-di-t-butyl-4-methylphenol and2,6-di-t-butyl-4-ethylphenol, 2,6-di-t-butyl-4-alkoxyphenols such as2,6-di-t-butyl-4-methoxyphenol and 2,6-di-t-butyl-4-ethoxyphenol,3,5-di-t-butyl-4-hydroxybenzylmercaptooctylacetate,alkyl-3-(3,5-di-t-butyl-4-hydroxyphenyl)propionates such asn-octadecyl-3-(3,5-di-t-butyl-4-hydroxyphenyl)propionate,n-butyl-3-(3,5-di-t-butyl-4-hydroxyphenyl)propionate and2′-ethylhexyl-3-(3,5-di-t-butyl-4-hydroxyphenyl)propionate,2,6-d-t-butyl-α-dimethylamino-p-cresol,2,2′-methylene-bis(4-alkyl-6-t-butylphenol) such as2,2′-methylenebis(4-methyl-6-t-butylphenol, and2,2-methylenebis(4-ethyl-6-t-butylphenol), bisphenols such as4,4′-butylidenebis(3-methyl-6-t-butylphenol,4,4′-methylenebis(2,6-di-t-butylphenol), 4,4′-bis(2,6-di-t-butylphenol),2,2-(di-p-hydroxyphenyl)propane,2,2-bis(3,5-di-t-butyl-4-hydroxyphenyl)propane,4,4′-cyclohexylidenebis(2,6-t-butylphenol),hexamethyleneglycol-bis[3-(3,5-di-t-butyl-4-hydroxyphenyl)propionate],triethyleneglycolbis[3-(3-t-butyl-4-hydroxy-5-methylphenyl)propionate],2,2′-thio-[diethyl-3-(3,5-di-t-butyl-4-hydroxyphenyl)propionate],3,9-bis{1,1-dimethyl-2-[3-(3-t-butyl-4-hydroxy-5-methyl-phenyl)propionyloxy]ethyl}2,4,8,10-tetraoxaspiro[5,5]undecane,4,4′-thiobis(3-methyl-6-t-butylphenol) and2,2′-thiobis(4,6-di-t-butylresorcinol), polyphenols such astetrakis[methylene-3-(3,5-di-t-butyl-4-hydroxyphenyl)propionate]methane,1,1,3-tris(2-methyl-4-hydroxy-5-t-butylphenyl)butane,1,3,5-trimethyl-2,4,6-tris(3,5-di-t-butyl-4-hydroxybenzyl)benzene,bis-[3,3′-bis(4′-hydroxy-3′-t-butylphenyl)butyric acid]glycol ester,2-(3′,5′-di-t-butyl-4-hydroxyphenyl)methyl-4-(2″,4″-di-t-butyl-3″-hydroxyphenyl)methyl-6-t-butylphenoland 2,6-bis(2′-hydroxy-3′-t-butyl-5′-methylbenzyl)-4-methylphenol, andp-t-butylphenol-formaldehyde condensates andp-t-butylphenol-acetaldehyde condensates.

Preferred phenolic antioxidants include those available under thefollowing trade designations: “Irganox L-135” (ex. Ciba SpecialtyChemicals Co.), “Yoshinox SS” (ex. Yoshitomi Seiyaku Co.), “AntageW-400” (ex. Kawaguchi Kagaku Co.), “Antage W-500” (ex. Kawaguchi KagakuCo.), “Antage W-300” (ex. Kawaguchi Kagaku Co.), “Irganox L109” (ex.Ciba Speciality Chemicals Co.), “Tominox 917” (ex. Yoshitomi SeiyakuCo.), “Irganox L115” (ex. Ciba Speciality Chemicals Co.), “SumilizerGA80” (ex. Sumitomo Kagaku), “Antage RC” (ex. Kawaguchi Kagaku Co.),“Irganox L101” (ex. Ciba Speciality Chemicals Co.), “Yoshinox 930” (ex.Yoshitomi Seiyaku Co.).

The lubricating oil composition of the present invention may comprisemixtures of one or more phenolic antioxidants with one or more aminicantioxidants.

In a preferred embodiment, the lubricating oil composition may comprisea single zinc dithiophosphate or a combination of two or more zincdithiophosphates as anti-wear additives, the or each zincdithiophosphate being selected from zinc dialkyl-, diaryl- oralkylaryl-dithiophosphates.

Zinc dithiophosphate is a well known additive in the art and may beconveniently represented by general formula II;

wherein R² to R⁵ may be the same or different and are each a primaryalkyl group containing from 1 to 20 carbon atoms preferably from 3 to 12carbon atoms, a secondary alkyl group containing from 3 to 20 carbonatoms, preferably from 3 to 12 carbon atoms, an aryl group or an arylgroup substituted with an alkyl group, said alkyl substituent containingfrom 1 to 20 carbon atoms preferably 3 to 18 carbon atoms.

Zinc dithiophosphate compounds in which R² to R⁵ are all different fromeach other can be used alone or in admixture with zinc dithiophosphatecompounds in which R² to R⁵ are all the same.

Preferably, the or each zinc dithiophosphate used in the presentinvention is a zinc dialkyl dithiophosphate.

Examples of suitable zinc dithiophosphates which are commerciallyavailable include those available ex. Lubrizol Corporation under thetrade designations “Lz 1097” and “Lz 1395”, those available ex. ChevronOronite under the trade designations “OLOA 267” and “OLOA 269R”, andthat available ex. Afton Chemical under the trade designation “HITEC7197”; zinc dithiophosphates such as those available ex. LubrizolCorporation under the trade designations “Lz 677A”, “Lz 1095” and “Lz1371”, that available ex. Chevron Oronite under the trade designation“OLOA 262” and that available ex. Afton Chemical under the tradedesignation “HITEC 7169”; and zinc dithiophosphates such as thoseavailable ex. Lubrizol Corporation under the trade designations “Lz1370” and

“Lz 1373” and that available ex. Chevron Oronite under the tradedesignation “OLOA 260”.

The lubricating oil composition according to the present invention maygenerally comprise in the range of from 0.4 to 1.2 wt. % of zincdithiophosphate, based on total weight of the lubricating oilcomposition.

Additional or alternative anti-wear additives may be conveniently usedin the composition of the present invention.

Typical detergents that may be used in the lubricating oil of thepresent invention include one or more salicylate and/or phenate and/orsulphonate detergents.

However, as metal organic and inorganic base salts which are used asdetergents can contribute to the sulphated ash content of a lubricatingoil composition, in a preferred embodiment of the present invention, theamounts of such additives are minimised.

Furthermore, in order to maintain a low sulphur level, salicylatedetergents are preferred.

Thus, in a preferred embodiment, the lubricating oil composition of thepresent invention may comprise one or more salicylate detergents.

In order to maintain the total sulphated ash content of the lubricatingoil composition of the present invention at a level of preferably notgreater than 2.0 wt. %, more preferably at a level of not greater than1.0 wt. % and most preferably at a level of not greater than 0.8 wt. %,based on the total weight of the lubricating oil composition, saiddetergents are preferably used in amounts in the range of 0.05 to 20.0wt. %, more preferably from 1.0 to 10.0 wt. % and most preferably in therange of from 2.0 to 5.0 wt. %, based on the total weight of thelubricating oil composition.

Furthermore, it is preferred that said detergents, independently, have aTBN (total base number) value in the range of from 10 to 500 mg.KOH/g,more preferably in the range of from 30 to 350 mg.KOH/g and mostpreferably in the range of from 50 to 300 mg.KOH/g, as measured by ISO3771.

The lubricating oil compositions of the present invention mayadditionally contain an ash-free dispersant which is preferably admixedin an amount in the range of from 5 to 15 wt. %, based on the totalweight of the lubricating oil composition.

Examples of ash-free dispersants which may be used include thepolyalkenyl succinimides and polyalkenyl succininic acid estersdisclosed in Japanese Patent Nos. 1367796, 1667140, 1302811 and 1743435.Preferred dispersants include borated succinimides.

Examples of viscosity index improvers which may be conveniently used inthe lubricating oil composition of the present invention include thestyrene-butadiene copolymers, styrene-isoprene stellate copolymers andthe polymethacrylate copolymer and ethylene-propylene copolymers. Suchviscosity index improvers may be conveniently employed in an amount inthe range of from 1 to 20 wt. %, based on the total weight of thelubricating oil composition.

Polymethacrylates may be conveniently employed in the lubricating oilcompositions of the present invention as effective pour pointdepressants.

Furthermore, compounds such as alkenyl succinic acid or ester moietiesthereof, benzotriazole-based compounds and thiodiazole-based compoundsmay be conveniently used in the lubricating oil composition of thepresent invention as corrosion inhibitors.

Compounds such as polysiloxanes, dimethyl polycyclohexane andpolyacrylates may be conveniently used in the lubricating oilcomposition of the present invention as defoaming agents.

Compounds which may be conveniently used in the lubricating oilcomposition of the present invention as seal fix or seal compatibilityagents include, for example, commercially available aromatic esters.

The lubricating compositions of the present invention may beconveniently prepared using conventional formulation techniques byadmixing base oil with the liquid crystal compound and one or moreadditives at a temperature of 60° C.

In another embodiment of the present invention, there is provided amethod of lubricating an internal combustion engine comprising applyinga lubricating oil composition as hereinbefore described thereto.

The present invention further provides the use of a lubricatingcomposition as described herein for reducing friction.

The present invention further provides the use of a lubricatingcomposition as described herein for reducing wear.

The present invention further provides the use of a lubricatingcomposition as described herein for improving fuel economy.

The present invention is described below with reference to the followingExamples, which are not intended to limit the scope of the presentinvention in any way.

EXAMPLES

Table 1 indicates the formulations that were tested. Said formulationswere manufactured by blending together the components using conventionalmixing techniques.

The Examples and Comparative Examples contained “America Core 600” asbase oil, commercially available from Exxon Mobil. The ComparativeExamples contained base oil only. The Examples according to the presentinvention contained 99 wt % base oil and 1 wt % T15(4-cyano-4′-pentyl-terphenyl commercially available from Alfa-Aesar).

Boundary friction coefficient measurements for the Examples andComparative Examples were obtained using a Plint TE-77 High FrequencyFriction Machine (commercially available from Phoenix Tribology). A pinon plate geometry was used. The test plate was annealed ground gage coldworked tool steel plate (AISI-01; maximum hardness of 20 on the RockwellC scale) surface ground in the direction of pin motion to a Ra roughnessof 0.35-0.45 μm. A 16×6 mm pin (polished high carbon steel, 60-63Rockwell C,) and was held in position on a moving arm against thestationary plate. Load was applied to the top of the reciprocating head.

A new test plate was placed in the specimen holder on the TE-77 with anew dowel pin placed in the movable arm. A few ml of lubricant wasplaced on the plate for each test (thin film lubrication). The testsequence was started. The TE-77 Friction Screener test conditions aresummarised in Table 1. Wear measurements on the cylinder were conductedby stylus profilometry. After profilometry data collection wascompleted, the “curved” surface of the pin was “flattened”, so that thecylinder wear appeared as an apparent wear volume (obtained bymultiplying the wear area times the wear length, μm³) and a maximum weardepth (nm).

TABLE 1 TE-77 Friction Screener Test Conditions Geometry Pin-on plateLower specimen Hardened ground gauge steel Upper specimen 16 × 6 mmhardened steel pin Load 100 N Temperature 130° C. Frequency 15 Hz StrokeLength 25 mm

The friction coefficient and wear measurements are shown in Table 2.

TABLE 2 Average Average Maximum Friction Wear Average Coefficient DepthWear Area Example (last 15 mins) (nm) (μm³) Comparative Example 0.09594636 633 1 (100 wt % base oil) Example 1 (99 wt % 0.0796 1239 204 baseoil + 1 wt % T15)

DISCUSSION

Table 2 shows that addition of 1 wt % of a liquid crystal terphenylcompound (T15) to a lubricating composition leads to a reduction infriction coefficient and wear.

We claim:
 1. A lubricating composition for use in the crankcase of anengine comprising a base oil and one or more additives, wherein thelubricating composition comprises from 0.01 wt % to 5 wt %, by weight ofthe lubricating composition, of one or more liquid crystal compounds,wherein the one or more liquid crystal compounds is a terphenylcompound.
 2. A lubricating composition according to claim 1 wherein theone or more liquid crystal compounds is present at a level of from 0.01wt % to 4 wt %, by weight of the lubricating composition.
 3. Lubricatingcomposition according to claim 1 or 2 wherein the one or more liquidcrystal compounds is present at a level of from 0.1 wt % to 2 wt %, byweight of the lubricating composition.
 4. Lubricating compositionaccording to any of claims 1 to 3 wherein the one or more liquid crystalcompounds is present at a level of from 0.2 wt % to 1 wt %, by weight ofthe lubricating composition.
 5. Lubricating composition according to anyof claims 1 to 4 wherein the one or more terphenyl compounds is acyano-substituted terphenyl compound.
 6. Lubricating compositionaccording to claim 5 wherein the cyano-substituted terphenyl compound isselected from alkylterphenylnitriles and alkyletherterphenylnitriles andmixtures thereof.
 7. Lubricating composition according to any of claims1 to 6 wherein the one or more terphenyl compounds is4-cyano-4′-pentylterphenyl.
 8. Use of a lubricating compositionaccording to any of claims 1 to 7 in the crankcase of an engine, inorder to reduce friction.
 9. Use of a lubricating composition accordingto any one of claims 1 to 7 in the crankcase of an engine, in order toreduce wear.
 10. Use of a lubricating composition according to any oneof claims 1 to 7 in the crankcase of an engine, in order to improve fueleconomy properties.